A conventional document scanning and recording device, such as a copier, can automatically determine size of a document placed on a platen. To this effect, laid-open Japanese patent application publication No. 11-231726 discloses that, width of the document is first detected and the size of the document is subsequently determined based on the detected width of the document.
FIG. 1A is a schematic diagram showing an A4 size document placed on a platen of a conventional copier. As shown in FIG. 1A, the conventional copier pre-scans a portion of the document and calculates a width dimension (width of short side) of the document. Given the fact that an A4 size sheet has the width dimension of 210 mm, the copier can determine whether or not the document on the platen is A4-sized based on the measured width dimension.